console.log(Math.floor(4.5));// 取下整 4
console.log(Math.ceil(4.5)); //取上整 5
console.log(Math.round(4.5)); //5
console.log(Math.trunc(4.5));  //截断 4
console.log(Math.pow(2,3)); // 2 的3 次方
console.log(Math.max(1,3,2)); //3
console.log(Math.min(1,3,2)); //1
console.log();


let num = Math.random() * 100;//[0,1)随机数 [0,100)
console.log(num);
console.log(num.toFixed(2)); //num(number) -> Number对象


console.log(parseInt("12.34px"));//12 解析成整数
console.log(parseFloat("12.34px"));// 12.34同上
console.log(Number("12.34px")); //NaN


console.log(num ===NaN);//f NaN 不等于任何值 包括自身
console.log(isNaN(num));//true 判断是否为NaN